linux-kernel - Re: [PATCH 2/7] x86: entry.S: simplify optimistic SYSRET

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Message-ID: <CAK1hOcNY5QYyHfLJNhR4BHg2S3re_VewSgwgB=xBL1m0VJFrug@mail.gmail.com>
Date:	Wed, 25 Feb 2015 01:31:54 +0100
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Denys Vlasenko <dvlasenk@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>, Oleg Nesterov <oleg@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Will Drewry <wad@...omium.org>,
	Kees Cook <keescook@...omium.org>, X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/7] x86: entry.S: simplify optimistic SYSRET

On Wed, Feb 25, 2015 at 1:04 AM, Andy Lutomirski <luto@...capital.net> wrote:
>> --- a/arch/x86/kernel/entry_64.S
>> +++ b/arch/x86/kernel/entry_64.S
>> @@ -756,9 +756,8 @@ retint_swapgs:              /* return to user-space */
>>          */
>>  irq_return_via_sysret:
>>         CFI_REMEMBER_STATE
>> -       RESTORE_C_REGS
>> -       REMOVE_PT_GPREGS_FROM_STACK 8
>> -       movq (RSP-RIP)(%rsp),%rsp
>> +       RESTORE_C_REGS_EXCEPT_R11
>> +       movq RSP(%rsp),%rsp
>
> I think this needs a comment.

I assume you mean "a comment why r11 doesn't need restoring".
I sent patch v2.
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